Gears of Wars - Expired Ceritficate

Today, someone ask how to troubleshoot Gears of Wars game from my campus mailing list. He got error message:

you cannot run the game with modified executable code. please reinstall the game.

I googled. I found why this could be happen and how to resolve this problem from gearsforum. The problem is expired certificate. The certificate valid from from 1/6/2006 to 1/28/2009. To resolve this problem, changing your system time back before 1/28/2009. But this can make another problem. Changing your system time may cause problems with other software on your computer.